The invention relates to coding switches that generate binary signals representative of selected numbers inscribed on an encoding wheel and more particularly, to coding switches that employ a light emitting diode to illuminate a selected number on the wheel.
Coding switches are utilized in digital systems to generate binary signals corresponding to selected decimal numbers. A known coding switch utilizes a rotatively mounted encoding wheel to generate binary signals representative of numerals that are inscribed on a translucent peripheral wall of the wheel. A light emitting diode (LED) is provided to illuminate a selected numeral of the wheel.
The LED is mounted within the switch and is powered by means of wires that are connected to power input points of a printed circuit board of the switch. The wires are bent around the edge of the encoding wheel and are soldered to the printed circuit board.
The above-indicated LED power connection for the known switch is undesirable, since the LED power wires may interfere with the movement of the encoding wheel. Also, the wires may rub against the encoding wheel and thereby transmit undesirable vibrations to the LED when the encoding wheel is rotated. Moreover, if the wires rub against the wheel, it is likely that the wires will be either broken or shorted together.
The placement of the LED and the routing of its wires within the known switch also complicates the assembly process, since the wires must be soldered to the printed circuit board and bent around the wheel and the soldered wires, wheel and printed circuit board must then be positioned in a switch housing as a unit. Moreover, if the LED is damaged or is otherwise rendered inoperable, it may be replaced only by dismantling the entire switch.
Another coding switch is disclosed in a German Application No. G7715970. The switch utilizes an encoding wheel to generate signals representative of numbers inscribed on a translucent peripheral wall of the wheel. A light source is mounted within the hub of the wheel to illuminate a selected number on the peripheral wall.
The axially mounted light source vibrates as the wheel is rotated. The vibration may reduce the life of the light source and may also tend to break the power wires. Also, the light source is relatively distant from the peripheral wall of the encoding wheel and therefore, the source must be operated at an undesirably high power in order to illuminate the numbers of the wheel. The high power operation of the light source may reduce the life of the source and may also unduly heat and expand the components of the encoding wheel.
It may be necessary to increase the clearance between components in order to compensate for such heat-induced expansion. However, the increased clearance may adversely affect the precision of operation of the switch and may also result in an increased vibration of the switch and a corresponding decrease in the life of the light source. Moreover, the light source must be dimensioned relatively precisely to fit in the hub of the encoding wheel and therefore, it is expected that the source will be relatively expensive and that the range of commercially available replacements for the light source will be limited.
Accordingly, it is an object of the invention to provide a simple and relatively inexpensive coding switch with a light source that may be easily replaced without dismantling the switch.
A further object of the invention is to provide such a coding switch wherein the light source of the switch is a light emitting diode that may be operated at a relatively low power to satisfactorily illuminate symbols inscribed on a peripheral wall of an encoding wheel.
Another object of the invention is to provide a means for connecting the light emitting diode of a lighted coding switch so that the wires of the diode are not rubbed against moving components of the switch or exposed to undesirable stresses as the switch is operated.
A further object of the invention is to provide a lighted coding switch wherein the light emitting diode of the switch is not vibrated as the switch is operated.
If the power wires of a light emitting diode are supported in grooves at the back of a switch, the wires may be shorted together if the switch is pressed against conducting elements of an adjacent switch. For example, if switches are stacked, the exposed metallic areas of a circuit board of one switch may press against and short out the wires at the back of an adjacent switch. Also, the wires of a switch may rub together and short one another out.
Accordingly, it is a further object of the invention to provide a lighted coding switch with a back panel that separates the wires of a light emitting diode of the switch and covers the wires to prevent the wires from contacting metal components of an adjacent switch.
If lighted coding switches are arranged in a stacked relation, it is also desirable to space adjacent switches sufficiently far apart so that a desired switch may be operated without inadvertently operating an adjacent switch.
Accordingly, it is an object of the invention to provide a switch back plate that not only protects the power wires of a light emitting diode of the switch but also provides a means for spacing the switch a convenient distance from an adjacent switch.
If the light emitting diode of a lighted coding switch is positioned in a space defined between a peripheral wall of an encoding wheel and the hub of the wheel, the radial dimension of the wheel must be sufficiently large to accommodate the LED. Thus, if a substantial reduction in size is required for the switch and its encoding wheel, the indicated positioning of the LED will unduly limit the reduction in size that may be obtained.
Accordingly, it is an object of the invention to provide a means for positioning a light emitting diode of a lighted coding switch so that the dimensions of the switch may be reduced.